Light sources produce incoherent light (i.e., which has a phase that varies randomly with time and position) or coherent light (i.e., which has a phase that does not vary randomly with time and position). The vast majority of light is produced from incoherent light sources (e.g., halogen bulbs, incandescent lamps, LED lights, etc.). The most common form of coherent light is produced by light amplification by stimulated emission of radiation (i.e., laser).
Typically, lasers produce coherent light by either emitted light in a narrow, low-divergence beam, or converted light into coherent light with the help of optical components such as lenses. The coherent light produced by lasers can be a narrow wavelength spectrum (i.e., monochromatic light), a broad spectrum (i.e., polychromatic light), or in some instances at multiple distinct wavelengths simultaneously (i.e., selectively-chromatic light). Some techniques presently used enable diffusion of the coherent light produced by lasers. For example, a laser beam may pass through a diffuser to spread the beam. Similarly, apertures may be placed in front of light projected from a laser to enable only some of the light to pass through the aperture.
The first lasers were gas lasers. Gas lasers require large power sources and generate significant quantities of heat radiation. Presently, there are many forms of lasers (e.g., chemical lasers, excimer lasers, fiber-hosted lasers, photonic crystal lasers, dye lasers, and free electron lasers). However, the advent of solid state lasers and semiconductor lasers have yielded commercial laser diodes capable of emitting coherent light at wavelengths from 375 nm to 1800 nm (and in some instances wavelengths of over 3 μm). These low power laser diodes only require 1 mW to 250 mW of power. Because of their extremely low energy requirements laser diodes have yielded numerous technological breakthroughs, such as, CD players, DVD Players, Laser pointers, laser printers, and numerous other devices. However, there are still many technological breakthroughs that have yet to be yielded by these low energy diodes.
Presently, the United States and the world are making efforts to reduce energy consumption. For example, there has been a large push in recent years to switch from incandescent light bulbs to compact fluorescent lamps. Some have even begun using LED (Light Emitting Diode) lamps as an even more energy efficient light source than compact fluorescent lamps. While these innovations are a step in the right direction, there is still a need to investigate other means for reducing energy consumption.
For example, a large quantity of electrical energy is consumed in illuminating signs and other surfaces at night. Notably, in April of 2009, the lights reflected off the surfaces of the Leonard P. Zakim Bridge were reported to cost over $5,000 per month and were thereby shutdown indefinitely. Further, many signs on the roads require lighting by highly inefficient high powered bulbs. Even further, many residential and commercial properties use similar bulbs to reflect off interior and exterior surfaces. Illuminating all of these surfaces creates a large burden, both environmentally and financially, due to the energy consumed. Thus, a need exists to create an energy efficient illumination apparatus and method for illuminating surfaces.